Lecture 12 - energy part uno

is energy a nutrient

no

from what is energy derived from mainly

carbs

protein

fats

how is energy measured

by ability to heat by calorimetry

1 calorie will heat...

1 g of water by 1 C

what is the net energy system used for

expressing energy supply and requirements in diets

why is the net energy system used

more reliable than feed (gross) energy

T/F energy and feed (gross energy) = energy available to animal (net energy)

false they are not equal

net energy system measures energy lost through

digestion and metabolism

compare and contrast corn vs sawdust

gross energy is similar, but net energy is not

what are the 4 sections of the net energy system

gross energy GE

digestible energy DE

metabolize energy ME

net energy NE

describe digestible energy

gross energy GE - energy is feces FE

reqs collection of feces

uses bomb calorimetry

describe metabolizable energy measured

top down - digestible energy DE - energy is methane MtE - energy in urine UE

or

bottom up - energy dissipated through heat increment HE + energy retained in gain, milk, and conceptus RE

describe energy in methane MtE

measure methane produce in respiration chamber

apply book value for heat of combustion

no need for bomb calorimetry as value is constant

what is the heat of combustion of methane

-890.3 kJ/mol

describe urinary energy UE

collect urine by catheter or cup

bomb calorimetry req

describe heat energy

measured by isothermal calorimetry

how many sources of heat energy are there

2, but only 1 measurement

describe retained energy RE

measure gain, milk, conceptus

estimate energy density of these via bomb calorimetry or indirectly from chem composition or book balue

what are the sources of retained energy

gain, milk, conceptus

describe the comparative slaughter technique

applied to measure RE in gain for growing beef animals

cohort slaughtered and homogenized

energy content of gain determined by bomb calorimetry

how is net energy measured

top down - metabolizable energy ME - HE heat increment only

bottom up - energy dissipated via maintenance HE + energy retained in gain, milk, and conceptus RE

describe maintenance

energy needed for animal to stay alive and active

made up of 3 components

what are the 3 components of maintenance

basal metabolic rate

activity

thermoregulation

define basal metabolic rate

heat production achieved during fasting and minimal activity

how is basal metabolic rate measured

animal fasted and heat production measured by isothermal calorimetry

heat increment = 0 by definition

what are some examples of activity

standing, walking, running

describe activity as measured in net energy NE

estimate activity budget by type and duration

calculate heat production by activity budget via book values

how are the book values of activity measured

by measuring rise in heat production during activity

describe thermoregulation

energy expended

for heating when env. temp Te < lower critical temp Tlc

for cooling when Te > upper critical temp Tuc

no additional energy expended when Tlc < Te > Tuc

what is the thermoneutral zone

when Tlc < Te > Tuc

no additional energy expended to thermoregulate

can maintenance be measured via comparative slaughter technique

yes HE is measured at several levels of ME intake, HE extrapolated to ME intake

includes energy expended via BMR, activity, and thermoreg

define heat increment

difference in heat production between metabolizable energy ME and net energy NE

what are some reasons that heat increment isnt well define

due to work of eating, fermentation heat, and nutrition metabolism

describe work of eating

measure rise heat production

around 3% of ME for ruminants - higher for forages, lower for concentrates

describe work of eating in ruminants

around 3% of ME for ruminants - higher for forages, lower for concentrates

describe fermentation heat

measure heat production of digesta with isothermal calorimetry

or calculate enthalpy of reaction from measured substrates and products of fermentation

describe fermentation heat for ruminants

around 10% of ME - higher for forages, lower for concentrates

describe nutrient metabolism

measure increase in heat production when infusing nutrients into emptied rumen

what does heat increment determine

efficiency of ME use for NE (NE/ME)

varies by ME of diet

why is net energy bottom up the most troublesome of measurements

requires calorimeter, respiration chamber, or large # of slaughtered animals

all required values are rarely measured in 1 experiment

what percent of humans diet is ME

90%